1. Field of the Invention
The present invention relates to a variable optical attenuator for use in optical fiber communications and for use with optical network technology, and particularly to a variable optical attenuator with anamorphic prisms to realize a variable attenuation of optical power.
2. Description of Related Art
An optical attenuator is a passive optical component for reducing optical power propagating in an optical fiber, and may perform fixed or variable attenuation. Optical attenuators are widely used in optical transmission systems and optical networks.
Means for providing fixed attenuation are well known in the art, which generally utilize a medium of fixed optical density disposed between a signal input fiber and a signal output fiber. These media can comprise isolated material placed between the signal carrying fibers or can comprise a coating upon the terminal end of at least one of the signal carrying fibers.
In the past, variable attenuations have reduced signal levels by transmitting such signals through partially opaque optical filters, by obstructing a section of the signal with attenuation filter segments, by varying the orientation between signal input and output fibers, or by diminishing signal strength via reflecting from partially light absorbent elements.
For example, U.S. Pat. No. 4,591,231 describes an optical attenuator containing a disk having a plurality of openings with fixed, neutral density filters of differing optical density contained therein. By rotating the disk, a fixed density filter of a desired opacity can be introduced into the signal path, thereby attenuating a portion of the signal. Although effective for reducing signal strength, such a system is limited in that attenuation levels vary in a step-wise rather than a continuous manner.
As shown in FIG. 4, U.S. Pat. No. 4,989,938 discloses another variable attenuator 100, which comprises a housing 150 containing a first optical fiber connector 140, a first optical lens 160, a first connecting optical fiber 180, a second optical lens 200 separated from the first optical lens 160 by an optical coupling region, a second optical fiber connector 220, a second connecting optical fiber 240, an optical filter 260 and a reciprocating means 280. The optical filter 260 is a flexible film having an optical density gradient varying along its length, which is mounted in an orientation substantially orthogonal to the optical axis within the optical coupling space between each of lenses 160 and 200. The filter 260 is operably connected to the reciprocating means 280 to vary the vertical position of the filter 260. As the density of the filter 260 is a gradient along its length, such vertical movement serves to provide areas or regions of differing optical density that transmits and absorbs differing amounts of light, thereby providing a continuously variable filter means between the lenses 160 and 200. In this application, the design and the manufacture of the filter are difficult and complex, so as to make the cost of the attenuator high.
It is thus desirable to provide a variable optical attenuator for overcoming the above problems.
An object of present invention is to provide a variable optical attenuator having anamorphic prisms for expanding a light beam, and an optical baffle for blocking the light beam.
Another object of the present invention is to provide a simple and low-cost variable attenuator that operates easily.
To achieve the above objects, in accordance with the present invention, a variable optical attenuator comprises a base, an attenuating means, a first collimator retaining an input fiber and a second collimator retaining an output fiber.
The attenuating means comprises a first anamorphic prism, a second anamorphic prism, a third anamorphic prism, a forth anamorphic prism a carrier and an optical baffle. Each anamorphic prism has two unparallel opposite surfaces. The optical baffle is mounted in a slot defined in the carrier.
In assembly, the four anamorphic prisms are orderly arranged on the base between two collimators respectively held in two through holes defined in two opposite walls of the base. The first and second anamorphic prisms are symmetrically arranged to the forth and third anamorphic prisms. The optical baffle is driven to move into light beam which comes from the first collimator and is expanded by the first and second anamorphic prisms, then blocks one part of the light beam. Thereafter, another part of the light beam passes through the third and forth anamorphic prisms and shrinks to form a parallel light beam received by the second collimator. Thereby, one part of light is lost.
Other objects, advantages, and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.